Lead developer for Compiz, Sam Spilsbury, says he sees little need to develop Compiz for Wayland due to the increasing fragmentation of the Linux ecosystem. Spilsbury writes "What does compiz actually provide to users of these systems? [...] None of this functionality that user wants really depends on our compositing engine. There's nothing so special about our compositing engine that gives it a reason to exist [...] This is the real practical toll of fragmentation amongst the Linux ecosystem. It's not just that there are multiple implementations of the wheel. There are multiple implementations of entire cars which do almost the same thing, but a little different from everyone else. Some say this is the free software's greatest strength. Now that I know the personal and technical toll of fragmentation, I see it as its greatest weakness."

Windows, Android and osX are each also distributions. The fact that only Microsoft can legally produce and ship Windows distributions doesn't change that.

I can see the point you're trying to make, but I think it's a bit of the stretch for the very reasons you later explained:

Is there fragmentation within Canonical's standard Ubuntu build or within the bounds of any other distribution.. not so much. Perhaps around the same amount of fragmentation found within the bounds of the current Windows distribution version.

Which is why you wouldn't call Ubuntu and Xubuntu different distros any more than you'd call different releases of Windows as different distros.